Simple Low pass resonant filter for your lunetta

efabric · Joined: Jan 05, 2012 Posts: 19 Location: Caen, France

Hello,

I found a long time ago this schematic on the squarewaveparade website :
http://thesquarewaveparade.com/images/srlpf.jpg

It's a 1 opamp low pass filter.

I'm not sure, but I think therr's a little mistake in the In and Out jacks ground. Don't the input and output must be decoupled with capacitors ?
The virtual ground in the power supply (4,5v) is directly linked to the ground output and input.

I think it's false no ?
Thank you.

Psyingo · Joined: Jun 11, 2009 Posts: 242 Location: Canada

Yep, that's a classic sallen-key filter. Replace the dual gang pot with two vatrols for simple voltage control. That's my favorite filter topology.

richardc64

efabric · Joined: Jan 05, 2012 Posts: 19 Location: Caen, France

It's a little bit strange...

I'm planning to build my modular lunetta with various units : 5v CMOS and ?V opamp based analog circuits.

What is the good way for everything to work together ?

I have a nice working radial transformer regulated 10V power supply in my bench, and 5V regulators in my spare parts.

Do you thik I can use this 0V, +10V and +5V to power up my opamps ?
Can I use the same +5V to power the CMOS modules and the virtual ground of the opamps ? Is there a risk of parasitic digital noise in the analog path ?

Can you show me a diagram with the interconnections and the decoupling stages ?